Your router isn't the problem.. as long as the camera has a strong signal to it. The problem is your upload speed of your home internet. 1-2Mbit/s upload isn't bad, but it's not enough to stream 640x480 MJPEG at 25 fps (the max spec on your camera). That would require around 7-8Mbit/s (according to some calculations found online) and depending on quality. You would only be able to manage about 7-9 fps at 640x480... and that's assuming you can run at full upload bandwidth of 1-2Mbit/s.
Even 320x240 at 25fps is going to need about 2Mbit/s.
You're going to have to do one or more these:
-buy faster speed internet
-drop your frame rate (fps)
-drop your resolution from 640 to 320.

A different camera may offer better compressions such as MPEG4 or H.264.. but I'm sure they come at a higher price.